Vessel-turret assembly having radially guided bogie wheels

ABSTRACT

A vessel-turret assembly with an opening ( 3 ) in the hull of the vessel wherein a turret ( 4 ) is rotatably received. The axial bearings ( 8 ) between the hull structure and the turret have a number of circumferentially spaced bogies ( 12 ) running on raceways. Each of the bogies ( 12 ) is mounted on a displacement element such as an elastically deformable element. The bogie body may comprise a side plate with flange or shaft which in a hingepoint is hingedly attached to the hull structure. This point is located near or on the plane defined by the load bearing surfaces of the wheels. In this way a radial movement of the load bearing surfaces of the wheels. In this way a radial movement of the load bearing surfaces of the wheels due to the elastical deformable elements is prevented. Alternatively, each bogie may comprise one or more axial wheels for engaging the hull structure and/or the turret to prevent radial movement of the bogie structure at the position of the load bearing surface of the wheels. When the bogies are mounted on an elastically deformable element, the bogies can be easily exchanged by compression of this element followed by removal of the bogies.

BACKGROUND OF THE INVENTION

The invention relates to a vessel-turret assembly comprising a hullstructure for accommodating a turret, wherein bearing means are providedbetween said hull structure and said turret comprising axial bearingmeans supporting the weight of said turret, said axial bearing meanscomprising a raceway on either the hull structure or on the turret aswell as rolling members running on said raceway, the turret beingprovided with a collar, said rolling members comprising at least threecircumferentially spaced sets of bogies each comprising at least tworolling wheels rotating on shafts mounted in a bogie body comprising asupporting base structure which is connected to an attachment surface oneither the hull structure or on the collar of the turret, wherein theother one of the hull structure or collar is provided with said racewayand wherein a displacement element is placed between said bogie body andthe attachment surface.

Such a structure is generally known in the art. For offshoreapplications there is an increased tendency to the use of floatingstructures, such as vessels, to replace platforms for exploitation ofoil wells. One reason is the lower costs involved whilst the other oneis the possibility to provide a storage in the vessel proper.

To permit weathervaning of the vessel during connection with a sub seaoil well, a turret member is provided either inside the hull structureor at its bow or stern end. The vessel can rotate with regard to theturret and via the lower side of the turret, risers from one or more subsea oil wells are received. On top of the turret a swivel is providedrealizing a rotatable fluid connection between the turret and thevessel.

To optimize the use of sub sea oil wells and to optimize efficiency ofthe vessel the number of conduits extending through the turret as wellas their diameter is increasing. In addition, for optimizing theproduction of the oil field, fluids, such as gas or steam, are injected.

To increase efficiency more conduits are connected to one turret and/orthe diameter of each conduit is increased.

Consequently, there is an increasing need to larger diameter turrets.However, one of the limiting structural features is the axial bearingsupporting a turret in the hull structure.

Up to now roller bearings have been used. The maximum diameter for suchroller bearings is about 14 meters at the time being and the costsinvolved for such a bearing are high.

It must be borne in mind that at increasing the diameter of such bearingthe fitting tolerances of several of the bearing parts and associatedmachine accuracy has to remain very high.

Because these bearings are custom made it can take up to a year afterorder before such a bearing is delivered. This means that after failurea turret structure comprising such bearings will be out of serviceduring a considerable time.

It has been proposed to replace such a bearing by plain bearings. Forexample sliding pads could be used. Although it is less likely that suchbearings will be damaged and such bearings are much cheaper, theweathervaning properties of the vessel dramatically decrease. This meansthat during a first part of rotation of the vessel because of changingwind and waves the turret will move along with the vessel. The anchorchains connected to the turret are subjected to considerable rotationalforces which means that such chains, which are relatively heavy aresubject to interlink wear and consequently to unforeseen failure.

From WO 93/07049 a turret-assembly is known in which the turret in axialdirection is supported on a plurality of bearing arms which carry axialand radial bearing elements. The axial bearing elements are formed bybogie wheels which are supported on a double raceway on the vessel. Thebogie wheels are mounted in a bracket which is connected to the radialarms by means of a rubber filler which eliminates sliding movements inthe bearings of the wheels in the bogies and will help even out the loadon the wheels.

To each arm a support wheel is connected having its rotation axisaligned in the axial direction. The circumferential surface of the guidewheel runs along the hull structure. Even though movement of the turretin the radial direction can be prevented to a certain extent, it isstill possible that the bogie wheels may move relative to the raceways.This can lead to an increased wear and reduced service life. It istherefore an object of the present invention to allow for relativemovements of the turret and the hull structure, while maintaining anaccurately defined position of the load-bearing surfaces of the bogiewheels on the raceways.

The known construction has as a further disadvantage that in case offailure of a bogie, it will be difficult to replace. This will mean thatthe known turrets will be out of service for a relatively long time whenfailure of a bogie occurs.

SUMMARY OF THE INVENTION

The present invention also aims to provide an improved axial lowfriction bearing for a vessel-turret assembly which upon brake down canbe easily and rapidly removed and exchanged by a new bogie.

This aim is realized with a vessel-turret assembly as described abovewherein the bogie body comprises at least one side support membersubstantially perpendicular to the shafts of the wheels and guide meanscooperating on the one hand with the side support member or with theshaft of the wheels and on the other hand with the hull structure toreduce radial movement of the bogies substantially at the load-bearingsurface of the wheels. Because the guide means according to the presentinvention are connected the shaft or to an outer support member, such asa side plate of the bogies, they reduce radial movement of the bogiewheels on the raceways while still allowing for sufficient radialmovement of the bogie bodies with respect to the attachment surface bymeans of the displacement element. The displacement element may comprisea slide bearing, an elastomeric pad, or equivalent elements.

According to one embodiment of the vessel-turret assembly according tothe present invention the guide means comprise at least two guide wheelshaving a rotation axis extending in the axial direction, the guide wheelaxis being connected to either one of the hull structure or the outersupport member, the circumference of the guide wheel contacting theother one of the hull structure or the outer support member. Two guidewheels may be attached to an outside support member of the bogie body torun along the hull structure, one guide wheel being attached to an innerside support member of the bogie body proximal to the turret. In thisconstruction, a three-point support of each bogie body is achievedwhereby accurate positioning of the running surfaces of the wheels alongthe raceways is possible.

In a preferred embodiment, the guide means comprise an ear on the sidesupport member of the bogie body which is proximal to the hull structureor on the shaft of the wheels which are supported therein, which ear ina hingepoint is hingedly attached to the hull structure, the hingepointbeing located in or near a plane defined by the load-bearing surface ofthe wheels. By means of the hinging roll, the load-bearing surfaces ofthe wheels are accurately maintained parallel to the raceways, whereasthe other parts of the bogie body are allowed to move relative to theraceways.

In case the displacement element is formed by an elastically deformablepad, the bogie wheels can be easily removed and exchanged formaintenance purposes. By compression of the elastically deformableelement, the supporting base can be lifted away from the attachmentsurface, which can be present on the hull structure of the vessel. Useis made in this way of the elastical deformable element to provide forexchangeability of the individual bogies. In this manner an individualset of wheels can be easily and rapidly replaced for maintenancepurposes with a minimum down time for the vessel-turret assembly.

In one embodiment, the bogie body is releasably attached to two supportbeams which are mounted to the attachment surface in a releasablemanner, a clearance being formed between the support beams. By placing ajack in the clearance between the bogie body and the attachment surface,the bogie body can be lifted from the support beams by compression ofthe elastically deformable element. After removal of the support beamsfrom beneath the bogie body, the set of wheels can be lowered such thatthey run free from the raceway, and the bogie can be replaced.

To further increase the load bearing capacity of the bogies according toa preferred embodiment of the invention on each shaft of the bogie tworadially adjacent rolling means are provided. It is possible to use asingle raceway for two of such radially adjacent rollers but preferably(in view of costs and machine tolerances) two of such raceways arepositioned radially adjacent to each other.

To improve easy exchangeability of the bogies or parts thereof, thesebogies are preferably connected to the deck level of the opening in thehull structure.

The axial bearing means according to the invention support the load ofthe turret in the hull structure.

However, during heavy sea it is possible that the turret is subjected toa force urging it in upward direction. To prevent axial movement inupward direction according to a further preferred embodiment of theinvention the collar is provided at its upper end with further axialbearing means.

Because such further axial bearing means will usually only be effectiveunder extreme circumstances they can comprise plain bearings. Duringtemporarily loading of such further axial bearings there will usuallynot be any weathervaning.

To prevent the turret from contacting the wall of the opening in thehull structure according to a further embodiment radial bearing meansare provided. To retain accessibility of the axial bearing meansaccording to the invention such radial bearing means are preferablyprovided below the axial bearing means as described above.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be further elucidated referring to a preferredembodiment of the in which is described below and shown in the drawings,wherein:

FIG. 1 shows schematically in side view a vessel provided with a turretand swivel;

FIG. 2 shows an enlarged detail of FIG. 1 of several components of thevessel-turret assembly, some of which are shown in cross section;

FIG. 3 shows a top view of a number of bogies according to theinvention;

FIG. 4 shows in detail a radial view of a section of a bogie accordingto the invention;

FIG. 5 shows in detail a cross section of the bogie-collar according tothe invention;

FIG. 6 shows in detail a circumferential view of a bogie according tothe invention; and

FIG. 7 shows a cross section of the bogie-collar where the raceway ismounted on the hull structure.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 7 shows a cross section of the bogie-collar where the raceway ismounted on the hull structure.

In FIG. 1 a vessel is indicated by 1. It has to be understood thatinstead of a vessel any other floating structure can be used with theinvention. In the hull 2 of the vessel 1 an opening 3 is provided forreceiving a turret 4. It must be emphasized that turret 4 can also beaccommodated in a structure extending from the hull, for example at thebow or stern end of the vessel. At its lower end, located nearkeel-level of the hull structure, the turret 4 can be provided withquick disconnect means to which anchor chains 5 are connected as well asrisers 13. On top of the turret a swivel 7 is provided realizing fluidconnection between risers 13 and pipe lines on deck of vessel 1.

in FIG. 2 a detail is shown from the hull structure-turret. It can beseen that opening 3 is defined by wall 26 of which the upper part isindependent from the remaining portion of the vessel. Flexing of thevessel will not be transferred to the upper part of wall 26. Betweenupper part of wall 26 and collar 11, being the top part of turret 4,bearing means 8 acting in axial direction are provided. On top of wall26 several counter clamps 27 are provided circumferentially spacedaround collar 11. Between collar 11 and circumferential clamps 27 spacedbearing pads of axial bearing 9 are provided. If there is an upward urgeon turret 4 during heavy sea condition upward stroke of turret 4relative to the hull structure is restricted by the clearance betweenthe pads of bearing 9. Bearing 9 is a plain bearing.

Below axial bearing 8 radial bearing 10 is provided comprising a numberof wheels 29 rolling in a U-groove 28.

In FIGS. 3-6 details of axial bearings 8 are shown. From these figuresit is clear that a number of bogies 12 is connected to the upper side ofwall 26 or the lower side of clamp 27. This connection is through amounting structure 18 in which shafts 24 are provided on which rollingwheels 17 are rotatably fixed through roller bearings 16. Wheels 17 eachengage a raceway 14, 15 respectively. Each bogie comprises four wheels,two adjacent to each other, and one set in front of the other.

Mounting structure 18 is connected to attachment surface 26 through anelastomeric bearing 19, and a supporting base 20. Instead of anelastomeric bearing, a slide bearing having flat sliding surfaces may beused. Connection between supporting base 20 and attachment surface 26 isthrough shear key 21. Shear key 21 is received in removable supportbeams 22, releasably connected to supporting base 20.

Between the removable support beams 22 a clearance or cavity 23 isprovided for receiving a hydraulic flat jack which is not further shown.If such a flat jack is introduced and actuated, the elastomeric bearingelement 19 is compressed and the supporting base plate 20 is lifted fromthe support beams 22. Thereafter, the support beams 22 can be removedand the related bogie can be lowered and replaced by another bogiestructure. In this construction, the height of the bogie structure maybe about 1.5 m, the height of the clearance 23 being about 12 cm. Theweight of the total bogie structure may amount to about 10.000 kg.

From FIG. 3 it is clear that a considerable number of bogies can beused. If one or more of such bogies fail they can easily be replacedeven during adverse weather conditions. Because the bogies are arelatively cheap standardized product the costs will be relatively lowallowing for storage on the vessel, so that immediate replacement ispossible.

Through the provision of the elastomeric bearing 19 compensation ofinaccuracies during manufacturing or deformation of several of the partsduring service is easily effected.

Because of the position of the axial bearing means 8 according to theinvention removal of the bogies is not hampered by another structure ofthe vessel exceptly from the counter clamps 27. However, it should benoted that only a few of such counter clamps are provided and the spacein between them is easily accessible for replacement of the bogiestructure.

It is also possible to position the clamp 27 in the proximity of theradial bearing 10 to further improve the accessibility of the bogies 12.

FIG. 6 shows a view in the circumferential direction of a bogiestructure wherein the shafts 24 of the wheels 17 are mounted in two sideplates 30, 31. Directly on the shaft 24, a flange 32 is attached havinga hinge point 33. The hinge point 33 is located in the plane defined bythe load-bearing surfaces 35 of the wheels 17. In the hinge point 33,the flange 32 is pivotably connected to the vessel through a tie-rod 34.Hereby a radial displacement, in the direction of the shafts 24 of thewheels 17 is prevented. Still, the wheels 17 can move on the elastomericbearing 19 around the fixed hinge point 33 to accommodate for positionalvariations between the attachment surface 26 of the vessel and theracetracks of the load-bearing surfaces 35.

FIG. 7 shows the opposite arrangement of FIG. 5, namely the raceway ison the hull and the base supporting structure is on the collar.

Although the invention has been elucidated above referring to preferredembodiments at the time being it has to be understood that many changesare obvious for the person skilled in the art and within the range ofthe appended claims.

What is claimed is:
 1. Vessel-turret assembly comprising a hullstructure (2) for accommodating a turret (4), wherein bearing means areprovided between said hull structure and said turret, comprising axialbearing means (8) supporting the weight of said turret, said axialbearing means (8) comprising a raceway (14,15) on either the hullstructure or on the turret (4) as well as rolling members running onsaid raceway, the turret being provided with a collar (11), said rollingmembers comprising at least three circumferentially spaced sets ofbogies (12), each comprising at least two rolling wheels (17) rotatingon shafts (24) mounted in a bogie body (18), comprising a supportingbase structure (20) which is connected to an attachment surface (26) oneither the hull structure or on the collar of the turret, wherein theother one of the hull structure or collar is provided with said raceway(14,15), wherein between said bogie body and the attachment surface adisplacement element (19) is situated for allowing radial displacementof the bogie body with respect to the raceways, the bogie bodycomprising at least one side support member (30) substantiallyperpendicular to the shafts of the wheels and guide means (32,33,36)cooperating with the side support member (30) or with the shafts (24)and with the hull structure to reduce radial movement of the bogies (12)substantially at the load-bearing surface of the wheels. 2.Vessel-turret assembly according to claim 1, wherein the guide meanscomprise at least two guide wheels (36) having a rotation axis,extending in the axial direction, the guide wheel axis being connectedto either one of the hull structure or the side support member (30), thecircumference of the guide wheel contacting the other one of the hullstructure or the side support member (30).
 3. Vessel-turret assemblyaccording to claim 2, wherein two guide wheels are attached to an outerside support member, proximal to the hull structure, one guide wheelbeing attached to an inner side support member of the bogie body,proximal to the turret.
 4. Vessel-turret assembly according to claim 1wherein the guide means comprise an ear (32) on the side support memberor on the shafts (24) of the bogie body (18), proximal to the hullstructure, which ear in a hinge point (33) is hingedly attached to thehull structure, the hinge point being located in or near a plane definedby the load-bearing surface of the wheels.
 5. Vessel-turret assemblyaccording to claim 4, wherein the hinge point (33) is located above theshaft (24) of the wheels, preferably at the level of the load-bearingsurface.
 6. Vessel-turret assembly according to claim 4, wherein the ear(32) is releasably attached to the vessel via an arm (34) which with oneend is releasably connected to the hinge point (33) and with its otherend is connected to the hull structure.
 7. Vessel-turret assemblyaccording to claim 1, wherein the displacement element (19) comprises anelastically deformable element.
 8. Vessel-turret assembly according toclaim 1, wherein on each shaft on said body two adjacent rolling wheels(17) are provided.
 9. Vessel-turret assembly according to claim 8,wherein two adjacent raceways (14,15) for each of said adjacent rollingwheels are provided on the other of the hull structure or collar. 10.Vessel-turret assembly according to claim 1, wherein the bogies areconnected to the hull structure near deck level of an opening in thehull structure.
 11. Vessel-turret assembly according to claim 1, whereinthe collar is provided at its upper end with further axial bearing means(9).
 12. Vessel-turret assembly according to claim 11, wherein saidfurther axial bearing means comprise plain bearings.
 13. Vessel-turretassembly according to claim 1, wherein between said hull structure andsaid turret radial bearing means (10) are provided below said axialbearings (9).